The long-range objective of this study is to identify factors other than intraocular pressure which influence the susceptibility of an optic nerve to glaucomatous damage. Patients with open-angle glaucoma, low-tension glaucoma, and ocular hypertension will be investigated by a detailed ocular examination, including visual field plotting, applanation tonometry, stereoscopic photography of the optic disc, fluorescein angiography, tonography, color vision testing, and ocular pulse pressure recording. Detailed neurologic evaluation, for evidence of cerebral ischemia, will be carried out in patients with low-tension glaucoma.